1. Field of the Invention
The present invention relates to a method for quickly providing silicon micro-molds for the fabrication of mechanical micro-components, particularly mold having very high aspect ratios wherein the mold has lateral feature dimensions on the order of microns while also having depth dimensions on the order of hundreds of microns. Furthermore, the present invention provides a silicon mold that does not change dimension or distort due to water absorption and/or due to thermal cycling, as do prior art mold materials such as polymethylmethacrylate (“PMMA”).
2. Description of Related Art
A variety of methods are presently known for making microparts. U.S. Pat. No. 5,256,360 to Li, teaches the use of a precisely controlled micro-electrode discharge machine (EDM) to make the micro-filter mold and suggests the use of laser-beam micro-machining, or electron-beam micro-machining, as suitable alternative processes. However, Li ('360), also teaches that molds made using conventional integrated circuits (IC) processing and lithographic processes in silicon tend to incorporate high internal strain, are prone to damage, are expensive to produce, and thus not economical to manufacture.
Current methods for fabricating molds for LIGA micro-component rely on high fluence, high brightness x-ray sources, typically synchrotron generated x-rays that are carefully collimated and directed onto a pattern-forming lithographic mask that replicates the image of the mask pattern into a layer of polymethylmethacrylate (PMMA). X-rays falling onto the surface of the PMMA substrate disrupt the molecular bonding in the exposed region and render it sensitive to chemical attack. Thus, by carefully controlling the amount and spatial location of the x-ray radiation, very small and very detailed features can be reproduced in the PMMA substrate. This process, however, is slow and limited by the availability of the synchrotron sources having the necessary fluence to deeply penetrate the PMMA substrates used by those skilled in the art.
Another approach is clearly needed.
U.S. Pat. No. 5,501,893 to Laermer, et al. describes a lithographic technique for etching silicon, generally referred to as “anisotropic etching,” where it is possible to achieve deeply extending trenches while simultaneously providing side walls which are as nearly parallel and vertical as desired. In order to achieve these geometries it is necessary to allow etching to progress only on the bottom of the etched trench in the silicon substrate and not on the walls of the trench. In particular, Laermer ('893) teaches a two-stage process for alternately etching an exposed silicon surface in a reactive ion plasma followed by coating the etched surfaces with a thin polymerized layer, wherein the polymer coating serves to protect the wall surfaces of the trench from action of the plasma since these surfaces do not directly face the incoming flux of plasma ions. However, the polymer layer applied to the “floor” surface of the trench quickly breaks down in the presence of the ion bombardment since this surface directly faces the incoming ions. The polymer layer, therefore, forms a very effective etching “stop” on those edges or surfaces not directly in the path of the ion flux allowing for directional etching.
The process continues in this manner, alternating etching steps with coating steps, until the predetermined etching depth of the structures in the silicon substrate is reached.
The inventors have realized that such a process can be used to create template structures out of silicon wherein the template structures comprise the inverse 3-dimensional image of the desired micro-components. The etched silicon wafer can therefore be used as a plating micro-mold into which a metal can be deposited, thereby forming the useful micro-component parts.